Chemical amplification positive resist compositions are materials for forming patterns on substrates, i.e., these compositions generate acids by irradiation with radiations, such as far ultraviolet rays, on the irradiated areas and undergo reaction utilizing these acids as a catalyst. This reaction causes a difference in solubilities in a developing solution between the irradiated area and non-irradiated area with the actinic radiations, thereby enabling pattern formation.
When KrF excimer laser is used as an exposure light source, compositions mainly comprising a resin having a fundamental skeleton of poly(hydroxystyrene) which is small in absorption in wavelength region of 248 nm are used, therefore high sensitivity, high resolution and good pattern forming can be ensured as compared with the cases where conventional naphthoquinonediazide/novolak series resins are used.
However, when light sources having further shorter wavelength, e.g., an ArF excimer laser (193 nm), are used, since compounds having an aromatic group fundamentally have large absorption in wavelength region of 193 nm, even chemical amplification resist compositions are not sufficient.
The use of poly(meth)acrylate is described in J. Vac. Sci. Technol., B9, 3357 (1991) as a polymer having small absorption in wavelength region of 193 nm, however, this polymer is inferior to conventional phenolic resins having an aromatic group in resistance to dry etching generally performed in semiconductor manufacturing process.
A mixed acid generator comprising a specific sulfonium salt (an anion having from 1 to 15 carbon atoms) and a triarylsulfonium salt is disclosed in JP-A-00-292917 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), combination of a triphenylsulfonium salt of a perfluoroalkane sulfonic acid having from 4 to 8 carbon atoms and 2-alkyl-2-adamantyl (meth)acrylate is disclosed in JP-A-00-275845, and a mixed acid generator comprising a specific sulfonium salt (an anion having from 1 to 8 carbon atoms) and a triphenylsulfonium salt or iodonium salt of perfluoroalkane sulfonic acid having from 4 to 8 carbon atoms is disclosed in EP-A-1041442.
For coping with finer pattern-making, a transformed illumination method or a phase-shift mask is generally used, zonal illumination is used for a line-and-space pattern, and a half tone phase shift mask is used for a contact hole pattern in many cases.
It has been desired to obtain high resolution and broad defocus latitude when zonal illumination is used. “Wide defocus latitude” means that the fluctuation of line width by the shift of focus is small.
When a half tone phase shift mask is used, there is a problem of a side lobe caused by the dissolution of a pattern part with a trace amount of transmitted light, and the solution of this problem has been desired.
Further, p-hydroxystyrene resin for use in a KrF excimer laser resist interacts with an acid generator, in particular, an ionic compound, e.g., an onium salt, and improves the solubility of the acid generator, however, a resin having an acyclic hydrocarbon structure is very high in hydrophobicity and the interaction with an ionic compound such as an onium salt is difficult to occur. As a result, the solubility of an acid generator becomes low, resulting in the problem of particles being liable to be generated during storage of a resist solution.
There are other problems of hole pitch dependency, exposure margin, and the fluctuation of sensitivity due to storage with the lapse of time. Further, there arises a problem that the film stability inside or outside an irradiation apparatus with the lapse of time (PED) is deteriorated and the pattern dimension fluctuates.
“PED (Post Exposure Delay) stability” means the film stability in the case where a resist film is allowed to stand in or outside an irradiation apparatus during the period of time after irradiation and before heating.
There is a further problem in the uniformity of a decrease in a film by oxide etching of a resin.